The present invention relates to a technique for allowing accurate monitoring of the data transmitted among parts of an electronic machine where a processor(s), a memory circuit(s) and/or other parts of the electronic machine are interconnected through transmission lines.
Recent advancements in highly integrated single-chip semiconductor devices have made it possible to provide faster processing of more data. Semiconductor devices have thus found wide applications in various fields, and many products have been developed incorporating such semiconductor devices.
Some instances involving data processing within a semiconductor device require monitoring of the data streams through the device in order to, for example, check how efficiently the resources of the semiconductor device are utilized. More specifically, it may be better to monitor the reading and writing of data to and from a memory circuit (hereinafter, referred to as “access” to the memory circuit) under the control of a processor in the course of development of a software product, especially when the software product is expected to operate in cooperation with the semiconductor device. In such cases, knowledge about what data has been written in which location of which memory circuit and are read at what timing enables software developers to check how efficiently the memory circuit is being utilized.
When data is transmitted at high speeds with a semiconductor device operating at higher clock frequencies, terminating resistance should ideally equal the characteristic impedance of the transmission line in order to reduce effects of reflections. A proper impedance match is also important to obtain accurate results of monitoring. On the other hand, higher integration of the semiconductor circuit results in an increasing number of input and output terminals of the semiconductor device. Accordingly, it becomes more and more difficult to provide line termination circuits at all ends of all transmission lines. In addition, the semiconductor device consumes more power as the number of line termination circuits increases.
In light of these circumstances, transmission lines terminated at only one end have been used increasingly. For example, for the transmission line interconnecting a processor and a memory circuit, termination is typically placed only on the memory circuit. One reason for this is that placement of the termination adjacent to or within reasonable proximity to the processor is usually difficult due to the processor's relatively larger number of input/output terminals compared to those of the memory circuit.
However, the termination on one end will cause reflections from the non-terminated end and, consequently, the deformation of waveforms. The reflections affect the accuracy of monitoring when an attempt to monitor the data that comes from the terminated end is made in the vicinity of the line termination circuit. A possible solution for the problem of the reflection is to monitor the data near the non-terminated open end. The monitoring itself can be made on the open end with a doubling of the amplitude of the data but this solution is not feasible for the non-terminated ends where there is not enough physical space for a line termination circuit. In such a case, it becomes virtually impossible to monitor the data on the transmission line.
Therefore, an object of the present invention is to provide a technique for allowing accurate monitoring of the data transmitted among a plurality of parts of an electronic machine, which otherwise is difficult or virtually impossible.